1. Field of the Invention
The present invention relates generally to closure devices for containers, and more particularly, but not by way of limitation, to a manway hatch suitable for use in corrosive service.
2. Description of the Prior Art
A number of oilfield related services involve the use of corrosive fluids such as acid which must be transported to the well site in substantial volumes. The potentially hazardous nature of these fluids requires that great care be taken when transporting them over the public highways. Numerous regulations are in effect regarding the transport of such materials.
Typically, corrosive fluids for use in the servicing of oil wells are transported in metal tanks carried on the back of a truck or trailer. These tanks have manways therein with bolted flanges surrounding the manways. The manways are typically closed through the use of a metal manway cover such as that known as the Clay & Bailey Model 1890. The Clay & Bailey manway includes a base portion having a bolted flange adapted to be bolted to the flange surrounding the manway of the acid tank. A metal cover is connected by a hinge to the base portion. A plurality of cam locking arms fold over the metal cover when it is in a closed position to lock the same in place. The Clay & Bailey manway cover may have the inner surface thereof lined when used for corrosive service. Nevertheless, such a manway cover includes a number of intricately shaped metal components such as cams, latches, pins and the like which are subject to external corrosion.
The prior art also includes non-metallic containers for corrosive fluids. One example of such containers includes those sold by Poly Processing Company of Monroe, La., sold under the designation Transtore Tanks Series II. The Poly Processing Company tanks are manufactured from high density polyethylene and have integrally molded therewith access openings having a female thread within which is threadedly received a male threaded cover plug having hammer lugs molded on its external surface.
Another prior art non-metallic tank is that sold by Bonar Plastics under the designation Poly Payloader .RTM.. These containers have an integrally molded neck with external male threads defined thereon. A molded non-metallic cap screws onto the threaded neck to close the access opening.